1. Field
Example embodiments relate to light emitting devices and methods of manufacturing the light emitting devices, and more particularly, to light emitting devices based on gallium nitride (GaN) on a silicon substrate and methods of manufacturing the light emitting devices.
2 . Description of the Related Art
Nitride-based semiconductors such as gallium nitride (GaN) have been applied to light emitting devices (eg., blue-purple light emitting diodes (LEDs) or laser diodes) and to electronic devices that are high-speed switching devices and/or high output devices. GaN-based LEDs are mainly manufactured on 2-inch sapphire substrates with 4-inch sapphire substrates gradually seeing increased use.
In order to increase productivity (e.g., yield) of LEDs and reduce fabrication costs, substrates should be enlarged. However, a sapphire substrate is expensive. Additionally, it is difficult to maintain uniform semiconductor layers because the sapphire substrate may bend at a high temperature due to a low thermal conductivity of the sapphire substrate when large sized semiconductor layers are grown.
Recently, there is increased interest in using silicon substrates for GaN-based light emitting devices. A silicon substrate is cheaper than a sapphire substrate or a silicon carbide (SiC) substrate. A large silicon substrate (e.g., 12 inch diameter) may be used, reducing fabrication costs and increasing productivity of the light emitting devices. In addition, because the silicon substrate is conductive, electrodes may be formed on a lower surface of the silicon substrate. Thus, fabrication processes of the light emitting devices may be simplified. In addition, since the silicon substrate has a higher thermal conductivity than that of the sapphire substrate, the silicon substrate may bend less than the sapphire substrate under a high thin film growth temperature used in the formation of a GaN thin film. Thus, the GaN thin film has a relatively greater uniformity using a silicon substrate of about 8 inches in diameter.
Regardless of the above advantages, it is difficult to use a silicon substrate as a substrate for GaN-based light emitting devices because a high dislocation density and cracks may occur due to a difference in lattice constants and thermal expansion coefficients between the silicon substrate and the GaN thin film. In addition, the silicon substrate may absorb light emitted from a light emitting layer and an external quantum efficiency of an LED may be reduced.